JPH1173999A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery comprising a positive active material containing a lithium-contained composite oxide and an electrolyte chloride containing lithium and fluorine, wherein an initial discharge capacity is large and decrease in discharge capacity is small, even if charging/discharging is repeated. SOLUTION: A nonaqueous secondary battery comprises a positive active material composed of at least one kind which is selected among the kinds of a Li-Co composite oxide, a Li-Ni composite oxide, and a Li-Mn composite oxide, and an electrolyte consists of at least one kind of electrolytic salt containing lithium and fluorine. In the battery, Mg containing metal oxide particles whose BET specific surface area is equal to 30 m<2> /g or more and the moisture content (Karl Fischer value) is equal to 3000 ppm or less are set to exit therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a positive electrode active material selected from the group consisting of Li / Co-based composite oxides, Li-Ni-based composite oxides, and Li-Mn-based composite oxides, and a fluorine-containing active material. The present invention relates to a non-aqueous secondary battery containing at least one electrolyte salt, and more particularly to a non-aqueous secondary battery having excellent charge / discharge cycle characteristics.

[0002]

_2. Description of the Related Art In recent years, a non-aqueous secondary battery using LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like as a positive electrode active material of a non-aqueous secondary battery can extract a high voltage of 4V class. Attention has been paid to this. At this time, a lithium salt is used as the electrolyte salt. In this case, a lithium salt containing fluorine is preferably used as the electrolyte salt from the viewpoints of electric conductivity, electrochemical stability, safety and the like. However, when these positive electrode active materials and lithium salts are used, although the initial discharge capacity is considerably large, there is a problem that the discharge capacity is reduced by relatively small number of repetitions when charge and discharge are repeated.

Several proposals have been made to solve such a problem. For example, there is a method using composite particles composed of a Li-Mn composite oxide and alumina (Japanese Unexamined Patent Application Publication No.
-31407 gazette). However, it has been estimated that the action of alumina suppresses the decomposition of the Li-Mn-based composite oxide, makes it difficult for the electrolyte to decompose, and reduces the decrease in discharge capacity due to charge and discharge. When repeated, the decrease in the discharge capacity cannot be sufficiently suppressed. Although the purpose is different from this,
Japanese Patent Application Laid-Open Publication No. H11-15064 proposes a method of adding a large amount of a powder of magnesia, alumina, titania, or the like to an organic electrolytic solution to reduce the fluidity and solve the liquid leakage.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a non-aqueous secondary battery containing a positive electrode active material comprising a lithium-containing composite oxide and an electrolyte salt containing lithium and fluorine, having a large initial discharge capacity and a high charge capacity. It is an object of the present invention to provide a non-aqueous secondary battery in which the discharge capacity is less reduced even when the discharge is repeated.

[0005]

According to the present invention, there is provided (1) a non-aqueous secondary battery, wherein the positive electrode active material is a Li / Co-based composite oxide, a Li / Ni-based composite oxide, or a Li-Mn-based composite oxide. Wherein the electrolyte comprises an electrolyte containing at least one electrolyte salt containing lithium and fluorine, and has a BET specific surface area of 30 m in the battery.
² / g or more, water content (Karl Fischer value) 300
Non-aqueous secondary battery characterized by having 0 ppm or less of magnesium-containing metal oxide particles, (2)
The electrolyte salt is LiPF ₆ , LiBF ₄ , LiN (CF ₃ S
O ₂ ) ₂ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F
Is at least one ₉ SO ₃ (1) a non-aqueous secondary battery according, (3) magnesium-containing metal oxide is MgO and / or hydrotalcite compound (1) a non-aqueous secondary battery according, (4) The nonaqueous secondary battery according to (1), wherein the positive electrode is composed of a mixture of a positive electrode active material and magnesium-containing metal oxide particles, and (5) the electrolyte salt, wherein the electrolyte solution contains lithium and fluorine. The above object has been achieved by developing a nonaqueous secondary battery according to (1), wherein a composite electrolyte of an electrolyte composed of an organic solvent and magnesium-containing metal oxide particles is used.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous secondary battery of the present invention is characterized in that the positive electrode active material is at least one selected from the group consisting of a Li.Co-based composite oxide, a Li.Ni-based composite oxide, and a Li.Mn-based composite oxide. The lithium secondary battery is composed of one kind, and the electrolyte is composed of an electrolyte containing at least one kind of electrolyte salt containing lithium and fluorine. In the lithium secondary battery, the magnesium-containing metal oxide particles are added to an electrolyte containing lithium-based composite oxide particles and / or an electrolyte salt containing lithium and fluorine as a positive electrode active material, and the positive electrode of the battery and And / or each can be used as a composite electrolyte.
The magnesium-containing metal oxide particles can also be used as a composite with a negative electrode active material. However, when a material having a strong reducing action such as lithium metal or carbon is used as the negative electrode active material, the positive electrode active material or the electrolytic It is more preferable to mix or add with the liquid.

In the non-aqueous secondary battery of the present invention, at least one of a Li.Co composite oxide, a Li.Ni composite oxide, and a Li.Mn composite oxide is used as a positive electrode active material. In this case, Co, N in these composite oxides
It is also free to use a composite oxide in which i or Mn is partially replaced by another metal element. Particularly, Li.Mn composite oxide or Li.Mn in which a part of Mn is replaced by another metal element.
In the case of a Mn-based composite oxide, the effect of suppressing a decrease in discharge capacity upon repeated charge / discharge is remarkable. Examples of the Li.Mn composite oxide include spinel type LiMn ₂ O ₄ , LiMnO ₂ ,
Composite particles of Li ₂ MnO ₃ and MnO ₂ are exemplified.

In any case, as the electrolyte salt used in the electrolytic solution, a lithium salt containing fluorine exhibits an effect of suppressing a decrease in discharge capacity upon repeated charge and discharge.
For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ S
O ₂ ) ₂ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉
Although SO _{3 and the} like can be used, when the magnesium-containing metal oxide of the present invention is used, the effect is remarkable particularly in the case of LiPF ₆ which easily reacts with moisture brought into the battery.

The non-aqueous solvent of the electrolytic solution is not particularly limited as long as it can be used as a non-aqueous solvent for a battery, for example, it dissolves an electrolyte salt, is chemically and electrochemically stable, and is aprotic. Absent. For example, carbonates such as dimethyl carbonate, propylene carbonate and ethylene carbonate can be used.

The negative electrode active material used in the non-aqueous secondary battery of the present invention is not particularly limited as long as it is capable of reversibly inserting and extracting lithium. For example, lithium metal, a lithium alloy, a carbon material, a metal chalcogen compound, and the like can be used. As the current collector for the positive electrode and the negative electrode, a material having electron conductivity, electrochemical corrosion resistance, and a large specific surface area is preferable, and a generally used current collector can be used. For example, metals such as aluminum and copper can be used.

The magnesium-containing metal oxide particles used in the non-aqueous secondary battery of the present invention have a BET specific surface area of 3
It is necessary that the water content is not less than 0 m ² / g and the water content (Karl Fischer value) is not more than 3000 ppm. The present inventors presume that the cause of the decrease in discharge capacity during repeated charge / discharge is a decrease in battery activity due to elution of Co, Ni, and Mn in the positive electrode active material, and a magnesium-containing metal oxide is added. Thus, an attempt was made to prevent this elution, and although the mechanism of the reaction had not yet been sufficiently elucidated, it was possible to prevent a decrease in discharge capacity. At the time of charging, the electrolyte salt containing fluorine reacts with a minute amount of water brought into the battery and decomposes to generate fluorine or hydrofluoric acid, which elutes Co, Ni or Mn in the positive electrode active material. It may be the main cause of the decrease in discharge capacity. The present inventors have intensively studied this elution suppression method, selected magnesium-containing metal oxide particles as a compound capable of trapping both moisture and fluorine or hydrofluoric acid in the battery, and by allowing this to be present in the battery, It is considered that a decrease in the discharge capacity at the time of repeated charge and discharge was suppressed.

To sufficiently trap moisture in the battery and fluorine or hydrofluoric acid by-produced by the reaction, the magnesium-containing metal oxide particles to be blended have a BET specific surface area of 30%.
It is necessary to be at least m ² / g. Preferably, B
ET specific surface area of 50 m ² / g or more, more preferably 1
00 m ² / g or more. BET specific surface area is 30m ² /
If it is smaller than g, it is considered that the ability to trap moisture in the battery and fluorine or hydrofluoric acid as a by-product decreases.
In addition, in order not to cause a decrease in discharge capacity due to repeated charge and discharge, the water content of the magnesium-containing metal oxide particles needs to be 3000 ppm or less. Preferably, it is 2000 ppm or less, more preferably, 1000 ppm
ppm or less. If the water content of the magnesium metal oxide particles is more than 3000 ppm, the effect of blending the magnesium-containing metal oxide cannot be exerted because the water trapping ability in the battery is reduced. As a method for reducing the water content of the magnesium-containing metal oxide particles, any method may be used, but a method of performing heat treatment at 300 ° C. or higher, cooling in an atmosphere having a dew point of −30 ° C. or lower, and taking out is simple.

In the present invention, the addition amount of the magnesium-containing metal oxide particles is not particularly limited, but may be practically added or mixed with the upper limit of 50 wt% with respect to the positive electrode active material, the electrolytic solution or the negative electrode active material. it can. If the addition amount of the magnesium-containing metal oxide is too large, the discharge capacity per weight of the secondary battery becomes small, so it is preferably 0.1 to 30 wt%, more preferably 0.1 to 10 w%.
t%. The centrifugal sedimentation average particle diameter (secondary particle diameter) of the magnesium-containing metal oxide particles used in the present invention is preferably 10 μm or less, more preferably 5 μm or less. It is considered that if the centrifugal sedimentation particle diameter is larger than 10 μm, the efficiency of trapping moisture and fluorine or hydrofluoric acid in the battery is reduced.

The magnesium-containing metal oxide of the present invention has a BET specific surface area of 30 m ² / g or more, a water content of 3000 ppm or less, contains magnesium having a strong bonding force with fluorine, and does not release magnesium. Any metal oxide particles can be used. The method for producing the magnesium-containing metal oxide is not particularly limited, and any method may be used as long as it satisfies the above conditions. Examples of these metal oxides include magnesium oxide, hydrotalcite compounds, MgAl ₂ O ₄ , MgCr ₂ O ₄ , Mg ₂ SiO ₄
And the like. Particularly preferred are magnesium oxide and hydrotalcite compounds. These are both electrochemically stable, have the effect of trapping and stabilizing moisture and fluorine or hydrofluoric acid, and are considered to be effective metal oxides for the purpose of the present invention.

The term "hydrotalcite compound" as used herein means a solid solution of alumina in magnesium oxide, and has the general formula Mg _x Al _{1 -x} O _1.5-0.5x · nH ₂ O (0 <X <
This is represented by 1). Particularly preferred is Mg _0.7 Al _0.3 O _1.15 containing no water of crystallization. Mg _0.7 A
l _0.3 O _1.15 not only adsorbs halogen and water,
In addition, since metals other than alkali metals can also be trapped, they also serve to remove metal impurities.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. [Positive electrode] Lithium carbonate and manganese dioxide were mixed at a molar ratio of Li: Mn of 1: 2, and calcined in air at 750 ° C. for 20 hours to obtain a spinel type LiMn ₂ O ₄ powder. L obtained
iMn ₂ O ₄ powder alone or mixed powder with magnesium-containing metal oxide particles, acetylene black as a conductive agent, and fluororesin powder as a binder are mixed at a weight ratio of 8: 1: 1, and this mixture is mixed. A positive electrode was formed by pressure molding on a current collector made of aluminum expanded metal. [Negative electrode active material] Metallic lithium having a thickness of 0.6 mm was used.

[Electrolyte] LiPF ₆ was added to a mixture of propylene carbonate and dimethyl carbonate at a volume ratio of 1: 2.
Was dissolved at a concentration of 1 mol / liter or a composite electrolyte obtained by adding magnesium-containing metal oxide particles to this electrolyte. [Metal oxide particles] Magnesium oxide particles (Micromag 3-150, manufactured by Kyowa Chemical Co., Ltd.) having a BET specific surface area of 105 m ² / g and a centrifugal sedimentation average particle diameter of 3.1 μm, a BET specific surface area of 33 m ² / g, and a centrifugal sedimentation average particle diameter of 5 0.0 μm magnesium oxide particles (Micromag 3-30 manufactured by Kyowa Chemical Industry Co., Ltd.), B
5. ET specific surface area 135 m ² / g, centrifugal sedimentation average particle size
5 μm hydrotalcite compound particles Mg _0.7 Al
_0.3 O _1.15 (KW-2000 manufactured by Kyowa Chemical Industry Co., Ltd.) was used. Note that the magnesium-containing metal oxide particles have a temperature of 400 ° C to 80 ° C.
The water content was adjusted by heating at a temperature of 0 ° C, and the dew point was -50.
It was used after cooling to room temperature in an atmosphere of ° C. [Charge / Discharge Cycle Test] A 2016 type coin cell was prepared using a positive electrode, a negative electrode, a polypropylene separator, and an electrolytic solution, and had a current density of 0.5 mA / cm ² and an operating voltage of 4.
The charge / discharge was repeated at 4 V to 3.0 V, and the discharge capacity at the initial stage and after 30 cycles was measured.

(Example 1) Spinel type LiM as a positive electrode
Mikuromagu against n ₂ O ₄ powder 3-150 (water content 2
LiPF ₆ at a concentration of 1 mol / liter in a mixed solution obtained by adding metallic lithium as a negative electrode and propylene carbonate and dimethyl carbonate at a volume ratio of 1: 2 as an electrolytic solution. The dissolved one was used. (Example 2) Micromag 3-150 (water content 20
(00 ppm) was replaced with 10 wt%, and the same operation as in Example 1 was performed except that 30 wt% was used. (Example 3) Micromag 3-150 (water content 2000p)
pm), except that 5 wt% was added.

(Example 4) Spinel type LiM as a positive electrode
Mikuromagu against n ₂ O ₄ powder 3-150 (water content 2
000 ppm), metallic lithium as the negative electrode, and micromag 3-15 as the electrolytic solution.
0 (water content: 2000 ppm) was carried out in the same manner as in Example 1 except that a composite electrolytic solution to which 5 wt% was added was used. (Example 5) Micromag 3-150 (water content 2000p)
pm) except that 15 wt% was used. (Example 6) Lithium carbonate, manganese dioxide, and nickel hydroxide were prepared at a molar ratio of Li: Mn: Ni of 1: 1.8: 0.
2 and calcined in air at 750 ° C. for 20 hours.
n _1. was obtained ₈ Ni _0.2 O ₄ powder. The operation was performed in the same manner as in Example 1 except that this LiMn _1.8 Ni _0.2 O ₄ powder was used as the positive electrode active material. (Example 7) Micromag 3-30 (water content 800 pp)
m) was carried out in the same manner as in Example 1 except that m) was used.

Example 8 KW-2000 (water content: 18)
(00 ppm) was used in the same manner as in Example 1. (Example 9) LiMn ₂ O ₄ powder, conductive agent,
A material composed of a binder was used, and metallic lithium was used as a negative electrode. Also, a composite electrolyte solution was used in which 5 wt% of Micromag 3-150 (water content: 2000 ppm) was added to the electrolyte solution. (Example 10) Micromag 3-150 (water content: 1000)
ppm) was used in the same manner as in Example 9. (Example 11) KW-2000 (water content: 1800 pp)
m) was performed in the same manner as in Example 9 except that m) was used. (Example 12) The same operation as in Example 1 was performed except that LiBF ₄ was used as an electrolyte salt.

Comparative Example 1 LiMn ₂ O ₄
A mixture comprising powder, a conductive agent and a binder, lithium metal as a negative electrode, and propylene carbonate and dimethyl carbonate as electrolytes mixed in a volume ratio of 1: 2 by LiP
The F ₆ was used after dissolved at a concentration of 1 mole / liter. (Comparative Example 2) BET specific surface area 150 m ² / g, water content 2
Example 1 except that 200 ppm alumina was used.
Was performed in the same manner as described above. (Comparative Example 3) Micromag 3-150 (water content 4000p)
pm), except that pm) was used.

[0022]

According to the present invention, the positive electrode active material comprises at least one selected from the group consisting of a Li-Co-based composite oxide, a Li-Ni-based composite oxide, and a Li-Mn-based composite oxide. In a nonaqueous secondary battery comprising an electrolyte containing at least one electrolyte salt containing fluorine, the positive electrode and / or the electrolyte have a BET specific surface area of 30 m ² / g or more and a water content (Karl Fischer value) of 3000 ppm.
The presence of the following magnesium-containing metal oxide particles succeeded in producing a nonaqueous secondary battery having a large initial discharge capacity and a small decrease in discharge capacity even after repeated charge and discharge. Despite the fact that conventional lithium-based non-aqueous rechargeable batteries were capable of extracting high voltage, a major problem was that the discharge capacity was reduced by a small number of charges and discharges. Although the decrease rate has been proposed, the decrease in the initial discharge capacity is small in the case where the rate of decrease is small, and the problem that the rate of decrease in the discharge capacity is large when the initial discharge capacity is increased. A non-aqueous secondary battery having a small decrease in discharge capacity due to repetition of charge and discharge while maintaining the same has been developed.

[Table 1]

[Table 1]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 6/18 H01M 6/18 // C01F 5/02 C01F 5/02 7/14 7/14

Claims (5)

[Claims] In a non-aqueous secondary battery, the positive electrode active material is L
i-Co-based composite oxide, Li-Ni-based composite oxide, Li
At least one selected from Mn-based composite oxides, wherein the electrolyte contains lithium and fluorine;
Consisting of an electrolyte containing various kinds of electrolyte salts, and having BE
A non-aqueous secondary battery comprising magnesium-containing metal oxide particles having a T specific surface area of 30 m ² / g or more and a water content (Karl Fischer value) of 3000 ppm or less. 2. An electrolyte salt comprising LiPF ₆ , LiBF ₄ , L
iN (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiCF ₃ SO ₃
2. The non-aqueous secondary battery according to claim 1, wherein the non-aqueous secondary battery is at least one of LiC ₄ F ₉ SO ₃ . 3. The non-aqueous secondary battery according to claim 1, wherein the magnesium-containing metal oxide is MgO and / or a hydrotalcite compound. 4. The non-aqueous secondary battery according to claim 1, wherein the positive electrode comprises a mixture of a positive electrode active material and magnesium-containing metal oxide particles. 5. The non-aqueous secondary battery according to claim 1, wherein the electrolyte is a composite electrolyte of an electrolyte comprising an electrolyte salt containing lithium and fluorine and an organic solvent and magnesium-containing metal oxide particles. .